Plasmapheresis is a process of separating plasma from whole blood. The plasma-depleted blood is comprised principally of cellular components, e.g., red blood cells, white blood cells and platelets. Plasma is comprised largely of water, but also contains proteins and various other non-cellular compounds, both organic and inorganic.
Plasmapheresis is currently used to obtain plasma for various transfusion needs, e.g., preparation of fresh-frozen plasma for subsequent fractionation to obtain specific proteins such as serum albumin, to produce cell culture media, and for disease therapies involving either the replacement of plasma or removal of specific disease contributing factors from the plasma.
Plasmapheresis can be carried out by centrifugation or microfiltration. Microfiltration apparatus generally utilize microporous membranes. The pores are cell-retaining pores, that is, the pores substantially retain cellular components but allow plasma to pass through. Typically, cell-retaining pores are of substantially uniform diameter and are of a size within the range 0.1 to 1.0 micrometer, that is, between membranes the pore size is within this range, but in any single membrane the pores are of substantially the same size.
Various planar membrane devices are disclosed in the literature. These include various configurations of membranes and flow paths. In general, microporous hollow fibers are being increasingly used. Gurland et al., in a paper presented at the 1981 annual meeting of the American Society for Artificial Internal Organs, reported that three hollow fiber plasmapheresis modules were commercially available. These are the Plasmaflo 01, Plasmaflo 02 and Plasmaflux, the first two utilizing cellulose diacetate membranes with a maximum pore size of 0.2 .mu.m, and the third, utilizing polypropylene with a maximum pore size of 0.5 .mu.m. Other features are listed below.
______________________________________ Lumen Effective Effective Wall (inner diameter) length surface thickness Module (.mu.m) (cm) (M.sup.2) (.mu.m) ______________________________________ Plasma- 370 about 20 0.65 160 flo 01 Plasma- 330 about 20 0.5 60 flo 02 Plasma- 330 about 20 0.5 140 flux ______________________________________
"Continuous plasmapheresis", as the term is used herein, is the process of continuously separating plasma from whole blood. Thus, as the term is used herein, "continuous plasmapheresis", and the apparatus needed to carry out a continuous plasmapheresis, must be able to provide, from whole blood, sufficient plasma, for example, at least about 500 mL, in a relatively short time, for example, 15 minutes to 3 hours, without substantial fouling of the membrane pores. The whole blood used in this invention either can be provided directly by a donor or patient or it can first be collected from a donor or patient and subsequently introduced into the apparatus of this invention, for example,from a reservoir.
It is an object of this invention to provide a hollow fiber plasmapheresis module which provides a high rate of plasma collection per unit area of membrane and which thus requires a small extracorporeal blood volume and a small surface area of membrane material, considered a foreign material to the blood. Another object is to provide such a module which not only provides a high plasma flux but also a high hematocrit in the plasma-depleted fraction. A further object is to provide a module which can operate continuously for longer periods of time than conventional plasmapheresis modules, thus making it suitable for use in continuous plasmapheresis. Another object is to provide such a module which is easy to assemble and easy to use without making extensive adjustments. A further object is to provide a plasmapheresis process employing hollow fiber membranes. Other objects will become apparent hereinafter.